In The Difference Engine, the steam-powered Engines are property of the British Crown, under the rule of the illustrious Prime Minister Lord Byron, and the clackers are their operators. As often happens with these things, the French have their own competing technology, the Ordinateurs, to rival the Engines. However, the operators of the French Ordinateurs weren't called "claqueurs", as Webby might have us believe. A pity, because that would have been such a cool name for them.

Clackers are presumably so named because of onomatopoeia. Just imagine how noisy and clacky a steam-powered computer operating on punch cards must be.